Receptors for gastrointestinal hormones are characterized using molecular biology methods. Methods include preparation of cDNAs, isolation and screening clones of interest, pharmacologic characterization of cloned receptors, screening for related receptor subtypes, in situ hybridization studies of the receptor of interest, chimeric receptor studies, preparation of antibodies to the isolated receptors of interest and characterization of genetic elements regulating receptor synthesis. A. Cloning of the cholecystokinin (CCK) type A receptor (CCK(A) receptor). At least two classes of receptors mediate the action of CCK and the structurally related peptide, gastrin in the CNS and in peripheral tissues; a CCK(A) and a CCK(B)/gastrin subtype. The CCK(A) receptor mediates CCK effects in the CNS on satiety and peripheral physiologic effects such as gallbladder contraction and pancreatic secretion. In this study the CCK(A) receptor was purified to homogeneity from rat pancreas and partial peptide sequencing was obtained after chemical/enzymatic digestion. Using degenerate oligonucleotide primers, clones were identified which led to identification of the nucleotide sequence of the rat pancreatic CCK(A) receptor. The CCK(A) receptor has 444 amino acids and seven putative transmembrane domains suggesting its membership in the guanine nucleotide-binding regulatory protein-coupled receptor superfamily. In vitro transcripts of the cDNA clone were functionally expressed in Xenopus oocytes and displayed the expected agonist and antagonist specificity. B. Cloning of the CCK(B)/gastrin receptor. The CCK(B)/gastrin receptor is the principal receptor mediating the action of CCK on gastrointestinal motility, growth effects and is the predominant subtype in the CNS mediating such CNS effects as CCK-induced anxiety and analgesia. In this study using a CCK(A) receptor cDNA probe, under low stringency hybridization conditions to screen a rat brain cDNA library and a cDNA library from AR42J cells, a pancreatic human cell line which possesses CCK(B) receptors, a novel cDNA was identified. The cDNA sequence was identical in both tissues and encoded a 452 amino acid protein which has 48% identity to the CCK(A) receptor. This receptor contains seven transmembrane domains characteristic of G-protein coupled receptors. COS- 7 cells transfected with the novel cDNA demonstrated the pharmacology characteristic for a CCK(B)/gastrin receptor subtype.